Generally the primary carrier carries the essential signaling that is specific to the wireless communication device. The primary carrier exists in both the uplink and downlink directions. Thus, if there is only a single uplink component carrier, the primary cell (PCell) is on that component carrier. The network may assign different primary carriers to different wireless communication devices operating in the same sector or cell.
A network node uses a multi-carrier secondary cell (SCell) setup procedure to at least temporarily setup or release an SCell for a wireless communication device capable of multi-carrier operation. The SCell may be setup or released in the downlink, uplink, or both. Examples of commands that the network can use in the multi-carrier SCell setup procedure include Configuration of SCell(s), De-configuration of SCell(s), Activation of SCell(s), and Deactivation of SCell(s).
The configuration procedure is used by the serving radio network node (e.g eNode B in LTE) to configure a carrier aggregation capable wireless communication device with one or more SCells in the downlink, uplink, or both. The de-configuration procedure is used by the serving radio network node to de-configure or remove one or more already configured SCells in the downlink, uplink, or both. The configuration or de-configuration procedure can also be used to change the current multi-carrier configuration. For example, the number of SCells can be increased or decreased, or existing SCells can be swapped with new ones.
In contrast to a PCell, which is always activated, SCells may be activated and deactivated as needed. Specifically, the serving radio network node may initiate activation of one or more deactivated SCells or deactivation of one or more active SCells on the corresponding configured secondary carriers. The configured SCells are initially deactivated upon addition and after a cell change, such as a handover. In LTE, the activation and deactivation command is sent by the eNode B to the wireless device via a media access control—control element, MAC-CE. The deactivation of SCell saves the wireless communication device's battery power.
In response to receiving the command to activate or deactivate the SCell, the wireless device, which may also be termed user equipment (UE), must activate or deactivate the SCell within a specified minimum time requirement. For example, TS 36.133 release 10 defines certain SCell activation delay requirements. Specifically, upon receiving SCell activation command in subframe n, the wireless device shall be capable to transmit a valid channel state information, CSI, report and apply actions related to the activation command for the SCell being activated no later than in subframe n+24 provided the following conditions are met for the SCell: 1) during the period equal to max(5 measCycleSCell, 5 Discontinuous reception (DRX) cycles) before the reception of the SCell activation command, (a) the wireless communication device has sent a valid measurement report for the SCell being activated, and (b) the SCell being activated remains detectable according to the cell identification conditions, and 2) the SCell being activated also remains detectable during the SCell activation delay according to the cell identification conditions. Otherwise upon receiving the SCell activation command in subframe n, the wireless device shall be capable to transmit a valid CSI report and apply actions related to the activation command for the SCell being activated no later than in subframe n+34 provided the SCell can be successfully detected on the first attempt.
The SCell deactivation delay requirements are also defined in TS 36.133 release 10. According to which, upon receiving SCell deactivation command or upon expiry of the sCellDeactivationTimer in subframe n, the wireless device shall accomplish the deactivation actions for the SCell being deactivated no later than in subframe n+8.
However, the activation or deactivation of one SCell may be interfered with by operations related to another SCell. For example, the activation or deactivation of a first SCell may be severely degraded when the wireless device receives a command to configure or deconfigure a second SCell while the wireless device is performing the activation or deactivation procedure for the first SCell.